Seismic Swarm S20100708.1: Analysis of Activity Near La Quinta, California

The seismic swarm designated S20100708.1 occurred in a tectonically active region of southern California, centered 22 km SSW of La Quinta in the Coachella Valley. This area lies within the San Andreas Fault system, where the Pacific and North American plates interact along multiple fault strands, including the Banning and Mission Creek faults. The swarm initiated at 02:32 on 7 July 2010 and concluded at 22:12 on 11 August 2010, spanning 859 hours and 40 minutes with a total of 1709 recorded earthquakes.

Geologically, the Coachella Valley forms part of the Salton Trough, a pull-apart basin resulting from right-lateral strike-slip motion. The region experiences frequent seismicity due to its position at the transition between the San Andreas Fault and the Imperial Fault zone. Depths of events in this swarm ranged primarily from 3 km to 16 km, consistent with the brittle-ductile transition zone in the upper crust of this transform boundary setting.

Examination of the first 100 events reveals a classic swarm pattern initiated by a magnitude 5.4 earthquake at 23:53 on 7 July 2010 at 12 km depth. This mainshock was immediately followed by several events of magnitude 2.7–3.0 within minutes, indicating rapid stress redistribution. Subsequent activity consisted predominantly of microearthquakes below magnitude 2.0, with depths clustering around 9–13 km. The sequence showed no single dominant aftershock decay but rather sustained low-level energy release over the initial hours.

Historical records indicate 12 swarms have occurred in the region since 1 January 2000. These include one swarm in 2001, two in 2002, two in 2003, two in 2005, two in 2009, and three in 2010. Such recurrent swarms highlight the area's propensity for clustered seismicity rather than isolated mainshock-aftershock sequences, likely driven by fluid migration or aseismic slip along fault segments.

This swarm underscores the importance of continuous monitoring in the Coachella Valley for understanding fault mechanics and assessing potential links to larger events on the San Andreas Fault.

References

USGS Earthquake Catalog California Geological Survey regional fault maps SeismoSight internal swarm classification data